The field of the invention relates generally to electric motors, and more specifically to a control system for hybrid operation of permanent split capacitor (PSC) motors.
At least some known variable speed compressor drive circuits use a permanent magnet (PM) motor and an inverter to operate the PM motor at variable speeds. However, the inverter may reduce motor efficiency by up to 6% at full load, may require power factor correction when operated at full power, and must be sized for extreme operating conditions to handle very hot climates. PSC motors on the other hand are slightly less efficient than PM motors but do not require an inverter at full load. They inherently have high power factor and low electromagnetic interference (EMI). However, PSC motors only operate at one speed. When operated at low load conditions, such PSC motors cannot reduce their speed to match the load demand, and render the system less efficient overall. Variable speed motor controllers exist that adapt motor speed for PSC motors to the load level, but the overall system suffers in term of full load efficiency due partly to the losses in the electronics, starting torque production, as well as power factor and electromagnetic interference